The dependence of calling activity in Rana esculenta Linné 1758 and Rana ridibunda Pallas 1771 upon exogenous factors (Ranidae, Anura).

The general weather situation distinctly influences the calling behaviour of both Rana esculenta and Rana ridibunda. The weather of the previous day or two previous days decides whether the frogs call or not. Calling activity following overcast skies, rain or wind is low or non-existent. After one or two warm, sunny and not too rainy days the frogs call. Considerable factors in this are also the temperature of air and water. The lower temperature limit for calling activity lies at 12°C for the water. But the air temperature is also relevant. Sudden, relatively sharp drops in the air temperature result in the cessation of calling even where water temperature would undoubtedly allow it. When the air temperature recedes sharply to 13-15°C or in persistently cool weather the frogs crawl into the bed of the pool. Before the spawning period the frogs are more sensitive to changes in the weather than during this period itself. Rana esculenta and Rana ridibunda thus possess only a single calling period, which can be interrupted into several calling phases by exogenous factors. These calling phases are not to be equated with true endogenously controlled calling periods.